X-ray tube apparatus.



E. W. CALDWELL.

X-RAY TUBE APPARATUS.

APPLICATION FILED OCT. 12. 1915.

Z3 3 17 T: e- 2/ 24 29 L H /v A L 33 55 73 5/ 5/ 5 ,1' 5 1 NTOR ATTORNEY Patented May 29, 191?.

EUGENE w. CALDWELL, or NEW YORK, N. Y.

X-RAY-TUBE APPARATUS.

Application filed October 12, 1915. Serial No. 55,877.

To all whom it may concern:

Be it-known that I, EUGENE W. CALD- wnnn, a-resident of the city, county, and State of New York, have made a certain new and useful Invention Relating to X- Ray-Tube Apparatus, of which the following is a specification, taken in connection with the accompanying drawing, which forms part of the same.

This invention relatesespecially to X-ray tube apparatus in which the X-ray tube of any suitable type or construction may be of reduced size by reason of the cooling currents of air, and so forth, which are used in connection therewith. A sectional tube shield is preferably arranged to closely inclose the X-ray tube and may be formed of bakelite or other phenolic condensation compounds or other material having high insulating properties under considerable rise of temperature, the material having incorporated therewith a large proportion of salts of high atomic weight elements so as to make it opaque to the X-rays within reasonable limits of thickness and Weight. The shield may with advantage be formed with a longitudinal or circumferential seam at which the shield sections may make dovetail joints, and staggered inlet and outlet holes may also be provided for the circulation of gaseous cooling medium in close contact with the tube. A fibrous filter may with advantage be arranged to cooperate with the inlet holes adjacent the anode end of the tube to prevent undesirable settle ment or collection of dust on the tube walls and a vacuum or exhaust hose connection is preferably arranged at the other end of the tube shield adjacent its axis so'as to facilitate adjustment of the tube shield under service conditions. One section of the tube is preferably provided with an emission aperture and cooperating window of fibrous or other air tight material substantially transparent to X-rays and when the shield is formed in longitudinal sections supports are preferably arranged in the section containing the emission aperture and window so as to securely mount and support the tube in this section in proper cooperation with the window so that the adjustment may be maintained when the entire shield is assembled.

In the accompanying drawings showing in a somewhat diagrammatic way illustrative embodiments of the invention Figure 1 is a longitudinal section through one form of apparatus. 1

Fig. 2 is a transverse section thereof taken substantially along the line 22 of Fig. 1; an Fig. 3 is a longitudinal section showing a modification.

A desirable material for the shields, diaphragms and other protective coatings and Specification of Letters Patent. Patented May 29, 1917.

devices used in connection with X-ray apparatus may be secured by incorporating with a suitable insulating strong tough binder, which does not undesirably deteriorate under moderate increase of temperature, suitable salts or preferably mixtures of salts of the high atomic weight metals or elements which have the desired selective absorption for some particular kind of such radiation. By the use of salts of a number of such heavy elements, as for instance, lead, zinc, iron, barium, thorium, or other high atomic weight metal or element, advantage can be taken of the usual selective absorption of these materials and by using the salts of these heavy elements which have the most desirable insulating and other properties the electric insulation and dielec- -tric strength of the resulting material are high resistance. As much-as 50 or 75 percent. of such heavy element salts can be thoroughly mixed and then incorporated with bakelite or other phenolic condensation products or other plastic material preferably prior to its being molded and con-- verted into its rigid permanent form, as described in the Baekeland Patents 942,699 and 942,700, for instance. By the use of such plastic compositions, tube shields, diaphragms and other protective devices or coverings can be readily molded or formed and can then be converted into permanent durable form with a minimum of expense. Such X-ray protective compositions have much greater electric resistance and dielectric strength than metals, so that, for instance, tube shields of such material can be arranged to closely inclose' X-ray tubes' can thusbe made lighter than metal shields. Such protective compositions are also quite permanent under conditions of moderate eat, which do not destroy or greatly impair their permanence. of form or electric insulation or dielectric strength as com .pared with the heat changes in hard rubber or the like. A suitable composition may be formed, for instance, bymixing substantially equal parts of the oxids or sulfids of. lead, zinc, barium and thorium, and then incorporatin themwith such proportion of the bakelite composition that they form substantially 60 or 7-5 per cent. by weight of the entire protective composition which can be molded while in its heated plastic condition and readily made permanent by the usual conversion processes.

Fig. 1 shows a sectional X'-ray shield formed of such material and comprising the longitudinally divided sections 1, 2' which may with advantage be formed with dovetail joints, the rib or tongue .4 fitting into the dovetail recess 3' in these cooperat ing parts, although it is of course understood that any other desired arran ement can beused by which these parts pre erably overlap sufficiently to effectively prevent leakage of undesirable radiation from the tube 10' within, which may be of any desired type. and. construction. As shown the tube may comprise a glass body and arms 11", 12, the cathode 13 being suitably supported within the tube body and electri- -;cally connected with the projecting terminal 16 while the target 14 is electrically connected with the terminal 15 projecting at the end of the other arm of the tube. The tube shield is preferably so formed as to closely engage the tube and efiect the circulation of the cooling currents of air or other medium in close contact with the'tube so as to rapidly carry ofi the heat generated during the operation of the tube which may thus be made of greatly reduced size for the same character of work. The tube shield may, for'instance, comprise'the body v (iand the arms 5 having a thickness of half a an inch to an inch or so and preferably ar ranged as close to the tube body as is desirable in view of the electric and cooling conditions. Any suitable arrangement may be used to; efiect the circulation of the cooling medium, a suction system being preferable for many purposes. If desired, suitable staggered, thatis, zigzag or crooked inlet holes'28 may be formed in any convenient part of the tube shield and preferably located adjacent the anode end of the tube so as to secure a greater deposition of any remaining dust particles through electrostatic separating action. A suitable filter 29 formed of felt or other porous material may be arranged adjacent these inlet holes and may, for example, be located in a suitable recess 30 in shield end and held in place as by the retainer cap 31. A coopcrating exhaust or hose connection is preferably arranged adjacent the other end of the tube shield, a staggered outlet opening 26 being, if desired, formed in one of the tube sections and having an exhaust hose 27 arranged in connection therewith so as to be located adjacent the axis of the tube and interfere to a minimum extent with the angular adjustment of the tube and shield e which is usual under operating conditions.

is thus allowed to issue from the tube shield for utilization in any desired way and for some purposes it is desirable to have an adjustable or replaceable diaphragm connected with or suitably cooperating with the tube shield so as to further limit the extent of this emergent pencil of X-ra'ys'. A series of replaceable diaphragms 40 having the desired sizes of diaphragm apertures '41- formed therein may be mounted .in a suitable slot 42 formed or molded in the tube I shield adjacent the emission, aperture, instance, and these diaphragms may, if'desired,'be formed of similar salt impregnated bakelite or other phenolic condensation material of the same general character as used for the tube shield. For many purposes it is also desirable-to have a suitable observation window in the tube shield and for this purpose a thick piece of lead glass 9 may be mounted or molded within the shield body in any desired part thereof so as to ,allow the inspection of the inner working parts of the X-ray tube from time to time and for some purposes also it is desirabl'e to have a suitable protective coverfsuch as I the cover 49 of similar salt impregnatedbakelite or the like which may be pivoted about the pin L8 in the adj-acent "-shield body. In this way the cover maybe swung away from this observation window whenever inspection of the tube interior is desired and readily swung back into closedposition to further insure that no undesirable radiation passes through this apertureunder other conditions.

It is desirable to arrange spring contacts in one or more of the shield elements or sections so as to make contact with the tube terminals within and for this purpose contact springs may be mounted within the shield and electrically connected with binding posts or other connections on the outside of the tube for ready connection with the cooperating electrical apparatus. The contact spring 17 may be mounted in any suitable way within the shield section 1, for instance, so that it normally makes electrical contact with the tube terminal 15, and if desired the connecting screw or end 18 of a suitable binding post or connection 19 may serve to hold this spring contact in position and simultaneously connect it directly with the connection arranged in any suitable part of the outside of the tube shield. A similar spring contact 20 may be mountedwithin the shield section 1 adjacent its other end and similarly connected with the screw or portion 21 of the binding post or connection 22 on the outside of the tube so that this spring 20 always makes electrical contact with the terminal 16 of the X-ray tube. For some purposes also it is desirable to have suitable alining devices arranged in connection with one or both ends of the tube and this may be conveniently effected by using an alining screwor member, such. as

- 23, extending through the tube shield, so

that-by turning its the contact spring 20 is forced longitudinally in this way the longitudinal alinement of pro ecting portion 2-;

to the desired extent so as to control the X-ray tube and readily adjust its longitudinal position even under operating conditions. Yielding supports are preferably arranged inside the tube shield so as to cooperate with the extreme ends of the tube where it is not undply heated under operating conditions. Such supports may with convenience be formed of thin flexible sheets of bahelite or similar insulating material and as shown in Fig. 2 the supports 25 cemented or mounted within the shield section 1 are arranged to engage the adjacent arm 11 of the tube at a number of points so as to yieldingly hold it in position in connection with other suitable supporting devices. A cooperating support which enables the tube to be permanently mounted in proper alinement within the section 1 of the shield may comprise the resilient bakelite or other support 36 which may be in strip form and pivoted or hinged a out the pin 37 in the shield section. while its other end may be adjustably held against the tube by a sup-- porting screw 38. Thus both ends of the tube are definitely held in proper position in such a yielding manner as to 'minimize the possibility of breakage or injury under service conditions, when some considerable expansion or heat distortion naturally takes place. This arrangement furthermore makes it possible to first mount the tube in the shield section 1 and insure its proper alinement with the admission aperture and window before the cooperating shield section 2 is secured in position and preferably permanently secured to the cooperating shield section so that the tube and inclosingshield constitute a unit which need not be taken apart until the tube is worn out in some cases, the tubeshield thus mechanically protecting the fragile X-ray tube and greatly minimizing the chances of its accidental in jury. Another arrangement is shown in Fig. 3 in which the shield is formed with the similar joint preferably comprising the dovetail portions 33, which'serve to separate the shield sections 51, 52, one of which preferably contains the emission aperture 56 and airtight emission window 57 of fiber board or the like which as indicated may be made considerably larger than the useful cone of rays which is to be utilized, this emission aperture being preferably made ample to take care of accidental lack of adjustment of the tube within the shield or of irregularity in the tube construction or target location. .A. diaphragm may be adjustably mounted on the shield in any desired way to cut off the radiation which is not utilized and for some purposes it is desirable to have a diaphragm guide which is adjustably mounted on the shield so that any one of a number of replaceable diaphragms may be used in connection therewith. For this purpose the portions 58 of tne shield adjacent this emission aperture may be formed with suitable screw holes with which screws or attaching members, such as 60, may cooperate so as to hold down suitable washers on the diaphragm guide 59 which may be provided with enlarged'holes or slots 61 of ample size to allow the desired adjustment of this-diaphragmguide in any direction. The slot 62 formed in this guide may be so arranged as to accommodate the replaceable diaphragm 63 which may be slid into this slot so as to bring the restricted aperture 64 into the desired centralized position defining the pencil of rays which issue from the shield. In this way after the tube 11 is inserted in the shield and preferably clamped quite tightly at one end so that any heat expansion or distortion may take place at the other end where the tube is more loosely or yieldably held, the adjustable diaphragm guide may be secured in position so as to hold a diaphragm substantially centrally with respect to the target of the tube and then any desired size of diaphragm may be used in the guide according to the work being handled. For some purposes it is desirable to form the shield body of two sections 51, 52 originally molded with open ends and with an annular recess, such as 54, adjacent the ends in which suitable plugs or disks 53 of this impervious material may be mounted preferably after being permanently shield having high electrical resistance and dielectric strength and being formed with dovetail joints between its sections and with staggered inlet and outlet holes for the circulation of gaseous cooling medium in close contact with said X-ray tube, a filter cooperating with said inlet holes, said shield being provided with yielding insulating supports to cooperate with the arms of the X- ray tube, spring contacts in said shield to cooperate with the tube terminals, a trans parent observation window of lead glass substantially opaque to X-rays mounted in said shield, said shield being formed with an emission aperture for the useful X-rays and an air tight emission window mounted in said aperture.

6. In X-ray tube apparatus, a sectional tube shield adapted to closely and disengageably inclose an X-ray tube and formed of phenolic condensation material containing a large proportion of incorporated salts of high atomic weight elements having different selective absorption for. X-rays, said shield having high electrical resistance and dielectric strength and being formed with dovetail joints between its sections and with staggered inlet and outlet holes for the circulation of gaseous cooling medium in close contact with said X-ray tube, a filter cooperating with said inlet holes, said shield being provided with supports to cooperate with the X-ray tube, a transparent observation window substantially opaque to X-rays mounted in said shield, said shield being formed with an emission aperture for the useful X-rays and an air tight emission window mounted in said aperture;

7. In X-ray tube apparatus, a sectional tube shield adapted to closely and disengageably inclose an X-ray tube and formed of phenolic condensation material containing a large proportion of incorporated salts of high atomic weight elements having different selective absorption for X-rays, said shield having high electrical resistance and dielectric strength and being formed with dovetail joints between its sections and with inlet and outlet holes for the circulation of gaseous cooling medium in close contact with said X-ray tube, a filter cooperatin with said inlet holes, said shield being ormed with an emission aperture for the useful X- rays and an emission window mounted in said aperture.

8. In X-ray tube apparatus, a sectional tube shield adapted to closely and disengageab'ly inclose an X-ray tube and formed of phenolic condensation material containing incorporated salts of atomic weight elements, said shield having high electrical resistance, and dielectric strength and being formed with inlet and outlet holes for the circulation of gaseous cooling medium in close contact with said X-ray tube, a filter cooperat- .the positive circulation of tight ing with said 'inlet holes, said shield being formed with an emission aperture for the useful X-rays and an emission window mounted in said aperture.

9. In X-ray tube apparatus, a sectional tube shield adapted to closely and disengageably inclose an X-ray tube, said shield having high electrical resistance and dielectric strength and being formed with inlet and'outlet holes, cooperating means to effect gaseous cooling medium in close contact with said X-ray tube, said shield being sion aperture for the useful X-rays and means to render said aperture substantially air tight. i

10. In X-ray tube apparatus, a sectional tube shield adapted to closely inclose an X-ray tube and formed of bakelite containing a large proportion of incorporated salts of high atomic weight elements having different selective absorption for X-rays, said shield having high electric resistance and dielectric strength and means to effect the circulation of gaseous cooling medium through said shield in close contact with said X-ray tube, a transparent observation window of lead glass substantially opaque to X- rays mounted in said shield, said shield being formed with an emission aperture for the useful X-rays and an air tight non-conductive emission window mounted in'said aperture and an adjustable diaphragm cooperating with said aperture and formed of bakelite impregnated with such salts.

11. In X-ray tube apparatus, a sectional tube shield adapted to inclose an X-ray tube and formed of bakelite containing a large proportion of incorporated salts of high atomic weight elements having different selective absorption for X-rays, said shield having high electrical resistance and dielectric strength and means to effect the circulation of gaseous cooling medium through said shield in close contact with said X-ray tube, said shield beingv formed with an emission aperture for the useful X-rays and an airnon-conductive emission window mounted in said aperture and an adjustable diaphragm cooperating with said aperture and formed of bakelite impregnated with such salts.

12. In X-ray tube apparatus, a tube shield adapted to inclose an X-ray tube and containing a large proportion of in-. corporated salts of high atomic weight elements having different selective absorption for X-rays,-said shield having high electrical resistance and dielectric strength and means to effect the circulation of gaseous cooling medium through said shield in close contact with said X-ray tube, said shield beformed with an emis- V ing formed with an emission aperture for e adjustable diaphragm cooperating with said aperture and impregnated with such salts.

13. In X-ray tube apparatus, atube shield adapted to inclose an X-ray tube and containing a large proportion of incorporated salts of high atomic weight elements having different selective absorption for X-rays, said shield having high electrical resistance and dielectric strength and means to effect the circulation of gaseous cooling medium through said shield inclose contact with said X-ray tube, said shield being formed with an emission aperture for the useful X-rays and an air tight emission window mounted in said aperture.

14:. In X-ray tube apparatus, a tube shield adapted to inclose an X'-ray tube and containing incorporated salts of high atomic weight elements having different selective absorption for X-rays, said shield having high electrical resistance and dielectric strength and means to effect the circulation of gaseous cooling medium through said shield in close contact with said X-ray tube, said shield being formed with an emission aperture for the useful X-rays and an air tight emission window mounted in said aperture.

15. In X-ray tube apparatus, atube shield adapted to closely inclose an X-ray tube and containing incorporated salts of high atomic weight elements having diiferentv selective absorption for X-rays, said shield having high electrical resistance and dielectric strength andsaid shield being formed with an emission aperture for the useful X-rays.

16. In X-ray tube apparatus, a sectional tube shield adapted to closely inclose an X- ray tube and formed of bakelite phenolic condensation material containing at least fifty per cent. of incorporated salt of high atomic weight material capable of absorbing X-rays, said shield having high electrical resistance and dielectric and mechanical strength and being formed with interlocked joints between its sections, said shield being provided with yielding insulating supports adapted to cooperate with the arms of the X-ray tube and support the tube substantially centrally within said shield, spring contacts in said shield to cooperate with the tube terminals, an alining member to effect the longitudinal alinement of said tube'in said shield, said shield being formed with an emission aperture for the useful X-rays.

17. In X-ray tube apparatus, a sectional tube shield adapted to closely inclose an X- ray tube and formed of bakelite phenolic condensation material containing at least fifty per cent. of incorporated salt of high atomic, weight material capable of absorbing X-rays, said shield having high electrical resistance and dielectric and mechanical strength and being formed with interlocked joints between its sections, said shield being provided with yielding insulating supports adapted to cooperate with the arms of the X-ray tube and support the tubewithin said shield, said shield being formed with an emiss1on aperture for the useful X-rays.

18. In adapted to. inclose an X-ray tube and formed of bakelite phenolic condensation material containing at least fifty per cent. of

incorporated salt of high atomic weight material capable of absorbing X-rays, said shield having high electrical resistance and dielectric and mechanical strength, said shield being provided with yielding insulatlng supports adapted to cooperate .with the arms of theX-ray tube and support the tube within said shield, said shield-being formed with an emission. aperture for the useful X-rays.

19. In X-ray tube apparatus, atube shield adapted to inclose an X-ray tube and contalning at least fifty per cent. of incorporated salt of high atomic weight material capable of absorbing X-rays, said shield having considerable electrical resistance'and dielectric and mechanical strength.

20. In X-ray tube apparatus, atube shield X-ray tube apparatus, atube shield adapted to inclose an X-ray tube and con- 1 tainlng a considerable proportion of finely 22. In X-ray apparatus, a tough strong shielding member adapted to intercept and absorb undesirable Xflrays, having high electrical resistance and dielectric strength and formed of converted molded phenolic condensation material containing at least fifty per cent. of incorporated finely divided salts of high atomic weight material capable of diversely absorbingX-rays.

23. In X-ray apparatus, a tough, strong, shielding member ada ted to intercept and absorb undesirable -rays, having high electrical resistance and dielectric strength and formed of converted molded phenolic condensation material containing at least fifty per cent. of incorporated finely divided salt of high atomic weight material capable of absorbing X-rays.

24. In-X-ray apparatus, a tough, strong,

shielding member adapted to intercept and absorb undesirable X-rays having high electrical resistance and dielectric strength and formed of converted molded phenolic condensation material containing at least fifty per cent. of incorporated finely divided high atomic weight material capable of absorbing X-rays.

25. In X-ray apparatus, a strong shielding member adapted to intercept and absorb undesirable X-rays having high electrical resistance and dielectric strength and containing at least fifty per cent. of incorporated finely divided high atomic weight ma terial capable of absorbing X-rays.

26. In X-ray apparatus, a strong shielding member adapted to intercept and absorb undesirable X-rays, having high electrical resistance and dielectric strength and containing a considerable proportion of incorporated finely divided high atomic weight material capable of absorbing X- rays.

27.- The bakelite phenolic condensation material which is adapted for use for molding Xray tube shields, diaphragms or other protective devices or coverings, and

which contains between fifty and seventyfive per cent. of incorporated relatively insulating salts of diverse heavy atomic weight elements, and which is soft and plastic when heated and capable of being converted by heat and pressure into rigid permanent form in which it has high electric insulation and dielectric stren th and is capable of intercepting and absor ing X- rays.

28. The bakelite phenolic condensationmaterial which is adapted for use for molding X-ray tube shields, diaphragms or other protective devices or coverings, and which contains over forty per cent. of incorporated salts of diverse heavy atomic weight elements, and which is soft and plastic when heated and capable of being converted by heat and pressure into rigid permanent form in which it has high electric insulation and dielectric strength and is capable of intercepting and absorbing X-rays.

29. The phenolic condensation material which is adapted for use for molding X- ray tube shields, diaphragms or other protective devices or coverings, and which contains over thirty per cent. of incorporated salt of heavy atomic weight material, and which is soft and plastic when heated'and capable of being converted by heat and pressure into rigid permanent form in which it hashigh electric insulation and dielectric strength and is capable of intercepting and absorbing X-rays.

30. The bakelite phenolic condensation material which is adapted for use for molding X-ray tube shields, diaphragms or other protective devices or coverin and which contains over fifty per cent. 0 incorporated salts of heavy atomic weight elements, and

which is soft and plastic when heated and capable of being converted into rigid permanent form in which it has high electric insulation and dielectric strength and is capable of intercepting and absorbing X- rays. Q

31.- The phenolic condensation material whichis adapted for use for molding X-ray tube shields, diaphragms or other protective devices or coverings, and which contains over twenty per cent. of incorporated salt of heavy atomic weight material, and which is soft and plastic when heated and capable of being converted into rigid permanent form in which it has high electric insulation and dielectric strength and 'is capable of intercepting and absorbing X- rays.

32. In X-ray tube apparatus, an X-ray tube comprising a glass body and arms and projecting terminals in said arms, and a removable, sectional tube shield closely inclosing said X-ray tube and having high electrical resistance and dielectric strength and absorbing X-rays, said shield being formed with inlet and outlet holes for the circulation of gaseous cooling medium in close contact with said X-ray tube, a filter cooperating with said inlet holes, said shield being provided with supports to cooperate with the arms of the X-ray tube, said shield being formed with an emission aperture for the useful X-rays and an air-tight nonconductive emission window mounted in said aperture.

33. In X-ray tube apparatus, an X-ray tube comprising a glass body and arms and projecting terminals in said arms, and a removable, sectional tube shield closely in closing said X-ray tube and having high electrical resistance and dielectric strength and absorbing X-rays, said shield being formed with inlet and outlet holes for the circulation of gaseous cooling medium in close contact with said X-ray tube, a filter cooperating with said inlet holes, said shield being provided with supports to cooperate with the X-ray tube, said shield being formed with an emission aperture for the useful X-rays and an emission window mounted in said aperture.

34. In X-ray tube apparatus, a sectional tube shield adapted to closely and disengageably inclose an X-ray tube and formed with electric connections to supply the tube, said shield having high electrical resistance and dielectric strength and being formed with inlet and outlet holes for the circulation of gaseous cooling medium in close contact with said X-ray tube, a filter cotiperating with said inlet holes and held in place by a cap adjacent one of the shield connections, said shield being provided with supports to codperate with the Xray tube, said. shield being formed with an emission apertact with said X-ray tube, afilter coiiperat ing with saidinlet holes, said shield being formed with {an emission aperture for the. useful X-rays and an emission window mounted in said aperture.

36. In X-ray tube apparatus, a substantially inclosed sectional tube shield adapted to closel and disengageably inclose an X-ray th e and absorb undesirableradiation, said shield having high electrical resistance and ,dielectric strength and being I formed with inlet and outlet holes, coop erating means to efl'ect the positive circulationof gaseous cooling medium, said shield being formed with an emission aperture for the useful X-rays and an emission window mounted in said aperture to make-the same substantially air tight. I t

37. In X-ray tube apparatus, a substantially inclosed sectional tube shield adapted to closely and disengageably inclose an X-ray tube and absorb undesirable radiation, said shield having high electrical resistance and dielectric strength and being formed with dovetail joints between its sections and with inlet and outlet holes and a cooperating exhaust connection forthe circulation of gaseous cooling medium in close contact with said X-ray tube, a filter 00- operating with said inlet holes, said shield being formed with an emission "aperture for the useful X-rays and an emission window mounted in said aperture. v

38. In X-ray tube apparatus, a substantially inclosed sectional tube shield adapted to closely and disen ageably inclose an-.'

X-ray tube and absor undesirable radiation, said shield having high electrical-resistance and dielectric strength and being formed with inlet and outlet holes and a cooperating exhaust connection for the forced circulation of gaseous cooling medium, said.

shield being formed with an air tight emission window mounted in said aperture.

39. In X-ray tube apparatus, a substantially inclosed sectional tube shield substantially non-transparent to X-rays and adapt ed to closely and disengageably inclose an X-ray tube, said shield having high electrical resistance, and dielectric strengthand being'formed with restricted inlet and outlet holes 006 erating means to effect the positive circu ation of gaseous cooling medium in close contactwith said X-ray tube, said shield being formed with an emission aperture for the useful X-rays and means to render said aperture substantially air tight.

EUGENE w. CALDWELL. Witnesses: i I I HARRY L. DUNCAN, Jnssm B. KAY. 

